Transcript 幻灯片 1 - QUST

Chapter9
Approximate Methods for
Multicomponent,
Multistage Separations
Exercises
Exercise9.1
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A mixture of propionic and n-butyric acids,
which can be assumed to form ideal
solutions, is to be separated by distillation
into a distillate containing 95 mol% propionic
acid and a bottoms product containing 98
mol% n-butyric acid. Determine the type of
condenser to be used and estimate the
distillation column operating pressure
Exercise9.2
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For 15 minimum equilibrium stages at 250
psia, calculate and plot the percent recovery
of C3 in the distillate as a function of distillate
flow rate for the distillation of 1,000 lbmol/h of
a feed containing 3% C2, 20% C3, 37% nC4,
35% Cs, and 5% nC6 by moles. Obtain Kvalues from Figures2. 8 and 2.9.
Exercise9.3
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Calculate and plot the minimum external reflux ratio
and the minimum number of equilibrium stages
against percent product purity for the separation by
distillation of an equimolar bubble-point liquid feed of
isobutane/n-butane at 100 psia. The distillate is to
have the same iC4 purity as the bottoms is to have
nC4 purity. Consider percent purities from 90% to
99.99%. Discuss the significance of the results.
Exercise9.4
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Use the Fenske-Underwood-Gilliland shortcut
method to determine the reflux ratio required to
conduct the distillation operation indicated in Figure
9.25 if N/Nmin = 2.0, the average relative volatility =
1.11, and the feed is at the bubble-point temperature
at column feed-stage pressure. Assume that external
reflux equals internal reflux at the upper pinch zone.
Assume a total condenser and a partial reboiler.
Exercise9.5
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The hydrocarbon feed to a distillation column is a bubble-point
liquid at 300 psia with the mole fraction composition, C2 = 0.08,
C, = 0.15, nC4 = 0.20, nCs = 0.27, nC6 = 0.20, and nC7 = 0.10.
(a) For a sharp separation between nC4 and nC5 , determine
the column pressure and type of condenser if condenser outlet
temperature is 120°F.
(b) At total reflux, determine the separation for eight theoretical
stages overall, specifying 0.01 mole fraction nC4 in the bottoms
product.
(c) Determine the minimum reflux ratio for the separation in part
(b).
(d) Determine the number of theoretical stages at L/D ~ 1.5
times minimum using the Gilliland correlation. .
Exercise9.6
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One hundred kilogram-moles per hour of a three component bubble-point
mixture to be separated by distillation has the following composition:
Component
Mole Fraction
Relative k
A
0.4
5
B
0.2
3
C
0.4
1
(a) For a distillate rate of 60 kmol/h, five theoretical stage, and total reflux,
calculate the distillate and bottomsi- tions by the Fenske equation.
(b) Using the separation in part (a) for components B and C, determine the
minimum reflux and minimum boilup ratio by the Underwood equation.
(c) For an operating reflux ratio of 1.2 times the minimum, determine the
number of theoretical stages and the feed-stage location.
Exercise9.7
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One thousand kilogram-moles per hour of rich gas at
70°F with 25%, 15% C2, 25%, 20% C4, and 15%
nC5 by moles is to be absorbed by 500 kmol/h of
nC10 at 90°F in an absorber operating at 4 atm.
Calculate by the Kremser group method the percent
absorption of each component for: (a) Four
theoretical stages, (b) Ten theoretical stages, and (c)
Thirty theoretical stages. Use Figures 2.8 and 2.9 for
lvalues.